Conventionally, a circuit device, for example, a sensor circuit or a level shifter circuit, which performs a certain processing operation with respect to an input signal by referring to a reference voltage and outputs the result, has been used widely.
FIG. 34 is a block diagram showing a configuration of a conventional common sensor circuit. There are various types of conventional sensor circuits depending on detection objects, but generally a sensor circuit is composed of, mainly, a sensor section 90 and a comparator 80, as shown in FIG. 34. The sensor section 90 has a sensor element 91 that receives a sensor input g1 (light, temperature, pressure, etc.) corresponding to a detection object of the sensor circuit and feeds out a current or a voltage corresponding to the intensity of the sensor input g1. The current or the voltage fed out of the sensor element 91 is sampled and charged in a capacitor 92 for a certain period, and a sensor output g2 corresponding to the intensity of the sensor input g1 can be obtained. The sensor output g2 is fed to the comparator 80. In the comparator 80, the sensor output 2g is compared with a reference voltage Vref, whereby an intensity or the like of the sensor input g1 is determined.
In the foregoing sensor section 90, a switching control operation is carried out between switches 93 and 94 from one to the other appropriately, whereby the sensor output g2 as shown in FIG. 35 can be obtained. In the case of the sensor output g2 as shown in FIG. 35, the presence/absence of the sensor input g1 can be determined by comparing a peak potential during a sampling period with the reference voltage Vref, as shown in FIG. 36. As shown in FIG. 37, the reference voltage Vref may be set at a plurality of levels (Vref1 to Vref3 in this example) and the peak potential is compared with values of at the plurality of levels of the reference voltage sequentially, whereby the intensity or the like of the sensor input g1 can be determined also.
As shown in FIG. 38, a photo sensor has been proposed conventionally that improves accuracy of light reception by performing time-division switching control for switching a reference voltage fed to a comparator between a first reference voltage (Vref1) at a detection level and a second reference voltage (Vref2) at an excess level (see, e.g., JP 4 (1992)-147086 A (page 3, FIG. 2 thereof)).